Ammonia-oxidizing bacteria (AOB) and the effects of environmental characteristics on the AOB community distribution were investigated in the Songhua Lake in May, August, October and December of 2011. Profiles of the AOB communities were generated using denaturing gradient gel electrophoresis (DGGE) to assess the expression of 16S rRNA genes followed by DNA sequence analysis. The dominant AOB groups were affiliated with Nitrosomonas and Nitrosospira spp. The effects of environmental characteristics on the AOB community distribution were analyzed by the ordination technique of redundancy analysis. The environmental characteristics significantly influencing the AOB community structure were different in the four seasons. The suspended solids (SS), ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) differed in May, the pH, NH4+-N, NO3--N and total nitrogen (TN) differed in August, and the NH4+-N, DO and TN differed in December. None of the assessed environmental variables displayed heterogeneity in October. This study suggested that seasonal variation and nutrient differences might be responsible for the differences in the key environmental characteristics used to determine the distribution of the AOB communities in all seasons. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.